1. Field of the Invention
The present invention relates to a process for continuously casting a light alloy and to an apparatus for continuously casting a light alloy.
2. Description of the Related Art
A process for producing a light alloy ingot using a continuous casting apparatus which will be described below, is conventionally known as a process for continuously casting a light alloy (an aluminum alloy, a magnesium alloy or the like). The apparatus includes a cylindrical water-cooled casting mold which is disposed immediately below a spout having an upward-turned molten metal receiving port and a downward-turned molten metal outlet and which has an inside radius larger than that of the molten metal outlet, and a lubricating oil discharge passage provided below the spout to supply a lubricating oil to a portion between the water-cooled casting mold and the molten metal brought into contact with the water-cooled casting mold. In this case, a plurality of lubricating oil discharge passages are generally disposed in a circumferential direction of the water-cooled casting mold.
However, the above process suffers from the following problem: When the molten metal exits from the spout and flows downwards within the water-cooled casting mold, such a phenomenon occurs that just a small amount of an outer-circumferential portion of the molten metal enters outlets of some of the discharge passages, and then exits from each of the outlets and flows along an inner peripheral surface of the water-cooled casting mold. Due to this, an outer peripheral surface of a produced ingot is torn off, roughened as a casting skin and the like to provide a casting skin failure. This will further become noticeable, if a circumferential electromagnetic agitating force is applied to the molten metal.
On the other hand, the dynamic viscosity of the lubricating oil is varied remarkably depending on the temperature and cannot be constant in each of the discharge passages. For this reason, a difference between discharge resistances to the lubricating oil in the discharge passages is produced and as a result, the amount of lubricating oil fed out of each of the discharge passages is liable to be non-uniform. This also causes the casting skin failure.
There is also a conventionally known continuous casting apparatus which includes a cylindrical water-cooled casting mold having a vertically-turned axis, and a lubricating oil supply passageway having a plurality of discharge ports disposed in the vicinity of an annular upper end of the cylindrical water-cooled casting mold. In this case, each of the discharge ports has a predetermined length in a direction of discharging of a lubricating oil, and the amount of lubricating oil discharged is controlled by constricting each of the discharge ports.
When a molten metal is continuously supplied to the cylindrical water-cooled casting mold from above the casting mold, a non-solidified portion of the molten metal is intermittently converted into a solidified portion in an upper portion of the cylindrical water-cooled casting mold. For this reason, a vibration is produced in the pressure of the molten metal. If the amount of lubricating oil discharged is controlled in the discharge ports under such a situation, the following problem occurs: the vibration of the molten metal pressure is applied directly to the discharge ports, thereby casing the entering of the molten metal into the discharge ports and the attendant back flow of the lubricating oil. As a result, the lubricating oil is not uniformly discharged from each of the discharge ports, whereby the roughening of a casting skin of a produced ingot is produced. In an extreme case, a phenomenon that the solidified portion of the outer periphery of the ingot is broken to cause the non-solidified portion within the solidified portion to be leaked outside, namely, a situation that a break-out is generated to fail the casting, is brought about.
This problem is further noticieable, when the agitating force is applied to the molten metal, because a vibration attendant on the agitating force is added to the above-described vibration.